1. Field of the Invention
The present invention relates to a gas-mixture-nonuniformity acquisition apparatus for an internal combustion engine which acquires the degree of nonuniformity (hereinafter simply referred to as “nonuniformity”) of a gas mixture formed within a combustion chamber of the internal combustion engine through mixture of a cylinder interior gas (a gas having being taken into the combustion chamber) and injected fuel. The present invention also relates to a gas-mixture-state acquisition apparatus for an internal combustion engine which acquires the state of such a gas mixture by reference to the nonuniformity of the gas mixture.
2. Description of the Related Art
Accurate prediction of combustion noise, generated torque, etc. is important for combustion control of an internal combustion engine. Accurate prediction of combustion noise, generated torque, etc. requires accurate prediction of a heat generation rate (heat generation speed) within each combustion chamber in relation to crank angle. This heat generation rate depends on a reaction speed of fuel (fuel vapor) within a gas mixture formed in the combustion chamber, and the reaction speed of fuel greatly depends on the state (fuel concentration, temperature, etc.) of the gas mixture. Therefore, accurate prediction of the state of the gas mixture is needed for accurate prediction of the heat generation rate. There have been known various methods for predicting the state of gas mixture (see, for example, Japanese Patent Application Laid-Open (kokai) No. 2001-254645).
Incidentally, when a gas mixture formed within a combustion chamber is observed microscopically, the fuel concentration (fuel mass concentration) within the gas mixture changes in accordance with the position within a region occupied by the gas mixture. Therefore, the heat generation rate, which is greatly influenced by the fuel concentration within the gas mixture, also changes in accordance with the position within the region occupied by the gas mixture. In other words, since the fuel concentration of the gas mixture formed within the combustion chamber becomes nonuniform, the heat generation rate becomes nonuniform. As a result, conceivably, the heat generation rate within the entire combustion chamber is greatly influenced by the nonuniformity of the fuel concentration within the gas mixture.
From the above, accurately acquiring the nonuniformity of the fuel concentration within the gas mixture is considered to be important for accurate prediction of the heat generation rate (accordingly, combustion noise, generated torque, etc.). However, the above-mentioned publication does not describe the nonuniformity of fuel concentration within a gas mixture at all. Meanwhile, methods for accurately acquiring the nonuniformity of fuel concentration within a gas mixture have conventionally been described in various papers, etc.
However, any method requires solving a complicated differential equation using a probability density function or the like, and involves a huge calculation load. Accordingly, there has been desire for developing a method for accurately acquiring the nonuniformity of fuel concentration within a gas mixture through a relatively simple calculation which does not require solving a complicated differential equation or the like.